This invention relates to a scissors lift apparatus for work platforms and other similar scissor lift apparatus for elevating of substantial load support units.
Scissor lift apparatus is often employed for raising and lowering of work support structures. Thus, in construction, servicing of utility lines and other elevated equipment requires mobile lift apparatus which is collapsed for transport purposes between locations. The lift apparatus includes a powered lift platform for supporting of work personnel in an elevated location at a work site. Various forms of powered elevating equipment including telescoping booms, scissors lift apparatus and the like are used. Various scissors lift apparatus are shown in the prior art and reference may be made to U.S. Patents, as follows:
______________________________________ U.S. Pat. No. Inventor ______________________________________ 93,877 Haasz 366,365 Averberg 2,533,980 Weaver 3,558,103 Lodige 3,672,104 Luckey 3,700,070 King 3,970,349 Banys 3,991,857 Wolk et al 4,114,854 Clark 4,130,178 Smith, Jr. 4,171,120 Clark 4,175,644 Sikli 4,684,314 Luth 4,858,482 Knudsen ______________________________________
Typically, a pair of laterally spaced and similar scissor units are secured to a mobile chassis and to a platform. Hydraulic cylinder units are coupled between the base support and the first set of scissors to expand and contract the scissors lift apparatus. Generally, each scissor unit includes a plurality of scissors which are secured in stacked relationship for lifting and lowering of the platform. An alternative system has disclosed a plurality of single scissors in stacked relation for raising and lowering of the platform.
Because of the heavy loads encountered, the scissors in multiple scissor units are mounted with the arms of each scissor in alignment and collapsed downwardly on to each other to establish and maintain a reliable and stable support of the loads. The arms of each scissor are therefore substantial and generally formed of box-like beams. The collapsed position establishes a minimal vertical stored position equal to the stacked thickness of the arms in each scissor.
Various applications which require substantial elevations use three or more scissors interconnected in stacked relationship to obtain the necessary elevation. Although providing particularly satisfactory and stable supports, the scissors will generally have a very significant collapsed height. As a result, mobile units have a corresponding vertical height with a heavy top load. The stability of the unit, therefore, may present certain difficulties in transport, particularly over uneven or rough terrain.
U.S. Pat. No. 3,558,103 particularly discusses and notes that the scissors lift apparatus is desirably formed with a minimum vertical height in a collapsed position.
Generally, in the prior art of multiple section scissors lift systems used for elevating of load platforms and the like, a separate four wheel chassis is provided with various hydraulic and electrical sources and power supplies mounted to the chassis. The chassis is formed with an upper support structure generally of a length equal to the collapsed scissors lift apparatus and a width slightly greater than the width of the scissors lift apparatus. The power and control mechanism is located beneath the base support structure for the scissors lift apparatus. This further increases the overall vertical dimension of the collapsed apparatus.
Further, to minimize the overall width of the system of a mobile unit for convenient over-the-road transport, the base structure for the scissors lift apparatus is generally located above the tire level of the mobile apparatus. This also generates a usable spaced structure beneath the scissors lift support structure for storage of the power and control equipment.
Existing scissors lift apparatus with three and more scissor sections for positioning work platforms and the like has found significant commercial usage because of the support characteristics provided. There is a demand however for improved mobility and stability of the apparatus, particularly for a minimal height of the scissors lift apparatus in the collapsed or folded position for transport and the like.